Detailed explanation of the ten precautions in the design of the peripheral circuit of the single chip microcomputer
You can see that RST is high when the resistor R1=10k in the reset circuit, and RST is low when R1=50. It is obvious that R1=10k is wrong, and the microcontroller cannot work at all when it is in the reset state. . The reason for this is that because the RST pin contains a triode, there is a small amount of off current even in the off state. When R is very large, a weak off current is generated and a high level is generated. Usually red patch LED: voltage 1.6V-2.4V, current 2-20mA, brightness changes in 2-5mA, no change in brightness above 5mA. At this time, it can be realized by means of an expansion chip, such as the 38-decoder 74HC138 to expand The filter capacitor is divided into a high frequency filter capacitor and a low frequency filter capacitor. 1, high-frequency filter capacitors generally use 104 capacity (0.1uF), the purpose is to short-circuit high-frequency components to protect the device from high-frequency interference. Normal IC (integrated) devices are added between the power supply and ground to remove high frequency interference (air static electricity). 2, low-frequency filter capacitors generally use electrolytic capacitors (100uF), the purpose is to remove low-frequency ripple, store a part of energy, stabilize the power supply. Most of them are connected at the power interface, next to high-power components, such as: USB excuse, stepper motor, 1602 backlight display. The withstand voltage is at least 2 times higher than the maximum voltage of the system. 1, switch function: When LEDS6 is high, it is turned off, and when it is low, it is turned on. Calculation of current limiting resistor: When the collector current is I, the base current is I/100 (this involves amplification, the collector current is 100 times the base), the PN junction voltage is 0.7V, and R=(5-0.7) )/(I/100) 2, amplification: Collector current is 100 times the base current 3, level conversion: When the base is at a high level, the triode is turned on, and the wire on the right side is grounded low. When the base is at a low level, the transistor is turned off and the output is high. The number formed by the digital tube lighting is composed of a, b, c, d, e, f, e, dp (decimal point), and the font and truth table are as shown above. Due to the limited output of the microcontroller, when the load is large, additional driver chips are needed, such as 74HC245. Pull-up resistor selection principle 1. Considering the power saving and chip sinking current capacity should be large enough; the resistance is large and the current is small. 2. It should be small enough to ensure sufficient driving current; the resistance is small and the current is large. 3. For high speed circuits, excessive pull-up resistors may cause the edges to become flat. Comprehensive consideration: the common value of the pull-up resistor is selected from 1K to 10K, and the pull-down is the same. Pull-down resistor Pull-up is to clamp the indeterminate signal through a resistor at a high level, and pull it down. 1, level conversion, increase the output level parameter value. 2, OC gate must be added with a pull resistor to use. 3. Increase the drive capability of ordinary IO pins. 4. Pull down the anti-jamming on the floating pin. Crystal oscillator circuit 1, crystal oscillator selection: According to the actual system requirements, 6M, 12M, 11.0592M, 20M waiting 2, load capacitance: Connect two 10 to 30pF capacitors to the ground, usually 20pF. 3, multimeter to measure the crystal: Directly use the red pen to the crystal oscillator pin, the black pen to the GND, and measure the voltage. Reset circuit Reset Set the internal circuit of the microcontroller to a certain state, and initialize all the registers. The reset time of the 51 MCU is about 2 mechanical cycles, depending on the chip data sheet. Generally, by resetting the chip or resetting the circuit, the calculation of the specific resistance and capacitance parameters is searched by google. The button is also a mechanical device, which will produce jitter at the moment of pressing or releasing, as shown below: There are two ways to eliminate it: software de-shake and hardware de-shake. The hardware de-shake is based on the principle that the capacitor is short-circuited to the high-frequency signal. Software debounce is to detect a key to execute a delay program after the key is closed, and generate a delay of 5ms to 10ms, so that the state of the key is detected again after the leading edge jitter disappears. If the closed state level is still maintained, it is confirmed that there is a real key press. under. WEB Management System is to access the management interface of the OLT through the IP address with a browser. Web Management,Network Device,Olt Device,Fttb Fttx Equipment Shenzhen GL-COM Technology CO.,LTD. , https://www.szglcom.com
WEB (World Wide Web) is the global wide area network, also known as the World Wide Web. It is a global, dynamic interactive, cross-platform distributed graphics information system based on hypertext and HTTP. It is a network service built on the Internet. It provides a graphical, easy-to-access and intuitive interface for browsers to find and browse information on the Internet. The documents and hyperlinks in it organize the information nodes on the Internet into one for each other. Associated mesh structure.
In 1989, a team led by Tim Berners-Lee in CERN (European Institute of Particle Physics) submitted a new protocol for the Internet and a file system using the protocol. The team named this new system World Wide Web. The purpose is to enable scientists around the world to use the Internet to exchange their work documents.
This new system is designed to allow any user on the Internet to search and retrieve documents from the databases of many document service computers. At the end of 1990, the basic framework of this new system was developed and implemented on a computer in CERN. In 1991, the system was transplanted to other computer platforms and officially released.